Project Summary As a deadly disease lacking an FDA-approved targeted therapy, triple-negative breast cancer (TNBC) involves a complicated and entangled network of oncogenic processes in which long non-coding RNAs (lncRNAs), a novel class of regulatory RNA molecules, may play important roles. The proposed study will genetically exploit lncRNA-regulated cellular networks in TNBC to identify an improved therapeutic strategy. Our research has illuminated lncRNA involvement in TNBC metastasis and metabolic reprogramming. One lncRNA, LINK-A, is upregulated in TNBC and is negatively correlated with breast cancer patient outcomes. Tissue-specific expression of LINK-A in mouse mammary glands drives tumor development and lung metastasis, which shares morphological and transcriptional similarity to human TNBC. Furthermore, the expression of LINK- A facilities an immunosuppressive environment and profoundly impacts CD9+ T-cell infiltration via lncRNA- mediated antigenicity loss. Mechanistically, LINK-A concurrently activates multiple oncogenic signaling pathways and promotes TRIM71-dependent degradation of the peptide-loading complex, leading to impaired antigen presentation. Therefore, LINK-A transgenic mice should serve as a powerful tool for dissecting the molecular complexity of TNBC and assessing precise therapeutic formulations against TNBC. Since most pathway inhibitors in TNBC clinical trials have been unsuccessful, a lncRNA-directed therapeutic approach, with the appropriate combination of immunotherapy, may optimize the efficacy of therapies for TNBC. The long-term goal of the proposal is to demonstrate the molecular mechanisms of lncRNA-mediated antigenicity loss and immunosuppression so that improved strategies can be developed to reduce TNBC morbidity and mortality. Our central hypothesis is that LINK-A promotes the initiation and immunoresistance of breast cancer, which can be attenuated in vivo by a combinatorial treatment approach. We will address our hypothesis from following aspects: we will first define the underlying molecular mechanism of lncRNA-dependent antigenicity loss. We will then restore antigenicity by targeting lncRNA and lncRNA-related signaling events. Finally, we will ascertain the functional importance of lncRNAs in breast cancer tumorigenesis. Emerging evidence of the oncogenic involvement of lncRNAs, as well as their implicated roles in mediating immunosurveillance and immunosuppression, warrants further characterization of TNBC-specific lncRNAs and future applications that hinge on their activity. Our goal is to demonstrate that LINK-A, as a hallmark of TNBC, may serve as a diagnostic marker that predicts a cancer?s sensitivity to immunotherapy. Thus, a strategy that combines immune checkpoint blockers and lncRNA-based therapeutic strategies has the potential to significantly advance TNBC treatment. In the long run, these research findings will benefit the cancer community by introducing the robust clinical effects of targeting lncRNAs and a well-defined means of stratifying patients based on these oncogenic lncRNAs.